Vacuum pump



Dec. 24, 1963 w. A. LLOYD ETAL 3, 5,297

VACUUM PUMP Filed June 13, 1960 3 Sheets-Sheet 2 IN V ENTORS 7457/1212: 19. Z20 4 0367 1,475,058??- Dec. 24, 1963 w. A. LLOYD ETAL VACUUM PUMP 3 Sheets-Sheet 3 Filed June 15. 1960 0D S T w m M\ N\ Q m m n m k x m .w Q ma V m "T m w W o N z 7 m 5 0 (W I k 0 NM\, h m QMN E WW Q m F HH United States Patent M 3,115,297 VACUUM PUMP William A. Lloyd, Sunnyvale, and Robert L. Jepsen, Los Altos, Calif., assignors to Varian Associates, Paio Alto, Calif., a corporation of California Filed June 13, 196i Ser. No. 35,307 8 Claims. (Cl. 2130-49} This invention relates in general to electrical vacuum pumps and more particularly to cold cathode glow discharge devices, especially useful for pumping gases from within enclosed vessels to extremely low pressures on the order of 1 l0- mm. of Hg.

Such glow discharge devices have become known in the art as glow discharge getter ion pumps. The pumping elements of these pumps have usually been constructed of one or more anode structures disposed between and spaced-apart from two cathode plates of reactive material, the mode structure providing a plurality of parallel spaced-apart glow discharge paths extending normal to the cathode plates, in many instances formed by hollow cells. Each pumping element was immersed in a strong magnetic field directed perpendicular to the cathode plates and substantially coaxially of the discharge passages or cells of the anode. The anode was operated a few thousand volts more positive than the cathode plates resulting in the establishment of a plurality of glow discharges between the anode and the cathode plates whereby the cathode plates were bombarded with high speed ions thereby dislodging portions of the reactive cathode material. The disintegrated cathode material condensed upon the large area of the anode to getter gas molecules within the apparatus and thereby reduce the gas pressure therewithin.

Previous cold cathode glow discharge getter ion pumps have either had a vacuum tight envelope surrounding and closely spaced from the pumping element on all sides or have had a vacuum tight envelope defining an enlarged central chamber with a plurality of lesser chambers communicating therewith and extending outwardly therefrom in each of which a pumping element was positioned. In the first type of pump just mentioned, gas access between the pump and the chamber being evacuated was achieved by means of a single aperture in the pump envelope communicating directly with only a portion of the pumping element, the only additional volume of gas ever being provided to the pumping element being disposed on the sides of the pumping element in the direction of the magnetic field, thereby decreasing the effect of means producing the magnetic field. In the second type of pump mentioned, wherein pumping elements were located in the lesser chambers extending outwardly from the enlarged entral chamber, direct access was only provided to one side of each pumping element.

The pumping speed of these pumps was limited since large volumes of gas were not directly accessible to all sides of the pumping elements. Also, the arrangement of the magnets which provided the magnetic field for some of these devices prevented the provision of means to introduce greater volumes of gases adjacent the pumping elements without sacrificing magnetic field strength.

Furthermore, in many of the previous pumps it was difficult to replace the pumping elements of the pump when they no longer operated efliciently. In many pumps the pumping element could not be removed without destroying the vacuum envelope, and in others in which the pumping elements could be removed this could not be accomplished at the opening into the pump.

Also, since a great deal of material is sputtered within the vacuum envelope of the pump, the means for insulating the anode and the cathodes must be protected against 3,1 15,297 Patented Dec. 24, 1963 deposit of sputtered material to prevent leakage thereacross.

in the present invention a large amount of space is provided adjacent to substantially all of the pumping element of the glow discharge apparatus whereby the greatest volume of gas molecules which can be pumped by the device is supplied to the pumping element while still providing a strong uniform magnetic field for the device.

The principal object of the present invention is to provide a novel sputter ion vacuum pump having increased pumping speed which is relatively easy to build and service.

One feature of the present invention is the provision of a novel sputter ion vacuum pump wherein access is provided for a large volume of gas to substantially all or the pumping element in which gas molecules are pumped.

Another feature of the present invention is the provision of a novel sputter ion pump wherein gas access chambers located substantially outside the magnetic field of the pump provide access for a large volume of gas to substantially all of the pumping element in which gas molecules are pumped and strong magnetic fields are provided over the entire area of the pumping element.

Another feature of the present invention is the provision of a novel sputter ion vacuum pump with a novel insulating element between the anode and cathode thereof to prevent voltage leakage thereacross due to sputtered material deposited thereon.

Other features and advantages of the present invention will become more apparent upon a perusal of the following specification taken in connection with the accompanying drawing wherein:

PEG. 1 is an external side view, partially broken away, of a high speed vacuum pump utilizing features of the present invention,

FIG. 2 is a side cross-sectional view of a portion of the structure of FIG. 1 taken along line 2-2 in the direction of the arrows,

FIG. 3 is an enlarged fragmentary cross-sectional view of the portion of the structure of FIG. 1 delineated by the line 3-3,

H6. 4 is an isometric view of a high speed vacuum pump utilizing features of the present invention,

FIG. 5 is a top view, partially broken away, of the high speed vacuum pump shown in FIGS. 1 to 4,

FIG. 6 is a top view, partially broken away, of another high speed vacuum pump utilizing features of the present invention,

PEG. 7 is a cross-sectional view of a portion of the structure of FIG. 6 taken along line 77 in the direction of the arrows,

FIG. 8 is a cross-sectional view of still another high speed vacuum pump utilizing features of the present invention, and

FIG. 9 is a graph showing the relationship between the pumping speed and the conductance for a typical electrical vacuum pump.

Referring now to FIGS. l5 of the drawings, the pumping element 11 of a getter ion vacuum pump utilizing features of the present invention comprises a cellular anode 12 supported between and spaced from two parallel rectangular cathode plates 13. The cathode plates 13 may be made of any suitable gettering material such at titanium, magnesium, zirconium or chromium of suitable thickness such as inch. The individual cells making up the cellular or honeycomb-like anode 12 preferably have a depth greater than their characteristic transverse dimension, and their axial center line is preferably substantially in alignment with a magnetic field H which is directed sub- {J stantially transversely to the cathode plates 13 as described in detail below. The preferred characteristic transverse dimension for the individual cells is a function of the magnetic field intensity H and the applied voltage between the anode 12 and the cathode plates 13, but for a magnetic filed intensity of 1800 gauss it has been found that a characteristic transverse dimension of approximately a half inch provides good pumping speed. The cellular anode 12 is preferably made of the same material utilized for making the cathode plates 13 in order to minimize flaking of condensed sputtered cathode material produced by the cold cathode glow discharge in use.

The cathode plates 13' are supported in parallel spacedapart relation on metallic flanged brackets 14 by means of a machine screw 15 at each corner of the cathode plates 13. The cellular anode 12 is supported on the flanged brackets 14 parallel to and spaced between the cathode plates 13 by means of a plurality of insulator assemblies 16. The surface of the flanged brackets 14 is spaced from the cathode plates 13 in the regions which are not required for structural support thereby providing greater access to the ends of the pumping element 11 for the gas being pumped.

Each insulator assembly includes a cylindrical dielectric insulator body 17 as of, for example, alumina ceramic with end portions 18 of reduced diameter fitted through apertures in the flanged brackets 14 and the anode 12 and retained therein by retaining rings 19. The mid portion of each ceramic insulator 17 is provided with an enlarged diameter with an open re-entrant portion 21 facing the flanged bracket 14. The large diameter portion of the insulator 17 with the reentrant portion 21 therein is formed by an outwardly projecting annular shoulder which is provided at its outer extremity with an axially directed annular portion which forms the outside surface of the reentrant portion 21. A cup-shaped centrally bored insulator shield member 22 is disposed axially of and spaced apart from the sides of the insulator body 17 and surrounds the re-entrant portion 21 thereby preventing depositof sputter material on the insulator body therewithin. The insulator shield member 22 is preferably made of the same material as the cathode plates 13 to prevent flaking of condensed sputtered cathode material thereon. This insulator assembly provides shielded high voltage insulation in a very short distance.

The pumping element 11 is positioned within an envelope 23 as of, for example, stainless steel wherein access is provided to the pumping element for a large volume of the gas to be pumped. The envelope 23 includes a narrow, elongated central pumping chamber 24 slightly larger than the pumping assembly 11 with two broad side walls. Each of two opposed open elongated sides of the central chamber 24- communicates directly with a gas access chamber 25 the same length as the pumping chamber. The transverse cross-section of each gas access chamber 25 is a partially closed semicircle with the opening into the pumping chamber 24 occupying a portion of the flat side. The bottom ends of the pumping and gas access chambers 24 and 25 are closed by a plate 26 and the top ends are sealed to one end of a throat 27 which tapers to a cylindrical tube, the free inlet end of which is provided with a circular vacuum coupling flange 28 for connecting the pump to the volume being evacuated.

The pumping element 11 is located in the pumping chamber 24 of the envelope by means of a locating pin 29 in the bottom thereof which is adapted to engage an aperture in one of the brackets 14. A crossbar support 31 is provided across the opening between the central chamber 24 and each of the side chambers 25 and is provided with a raised portion 32 with a tapped hole therein whereby the other fianged bracket 14 of the pumping element 11 is positioned thereon and screwed thereto.

The pumping element could actually be comprised of a plurality of anodes and cathodes stacked parallel to one another and the broad side walls of the pumping chamber provided that the magnetic field H is made strong enough for proper glow discharge operation.

The smallest dimension of the inlet end of the throat 27 is larger than the width of the pumping element so that the pumping element 11 can be removed from the envelope 23' for repair or replacement. Removal can easily be accomplished since only the screws in the top flanged bracket 14- hold the pumping element in the envelope and these screws can be reached directly through the inlet opening into the pump.

With a large volume of gas directly accessible to the pumping element 11. by means of the gas access chambers 25' a sputter ion vacuum pump embodying the present invention utilizes the cold cathode discharge pumping characteristics of the pumping element 11 to the greatest degree possible.

A high voltage lead-in insulator 33 is provided in the throat 27 of the envelope 23 and is connected to the cellular anode 1 .2 to maintain the anode at a positive potential with respect to the two-spaced cathode plates 13 which for convenience are maintained at ground potential.

A uniform magnetic field H is provided perpendicular to the long surface of the cellular anode 12 in axial alignment with the cells thereof by an external magnet structure. The magnet structure includes two T shaped pole pieces, the top portion 34: of each pole piece being posi tioned adjacent and parallel to the external surface of one of the broad side walls of the pumping chamber 24- and held in place by a bolt through a flange 36 projecting outwardly from the side of the envelope 23. Pairs of oppositely directed U-shaped magnets 37 surround the envelope 23 and have their pole pieces of the same polarity bolted to the stem portions 35 of the T shaped pole pieces by means of long screws 38 and bolts 39 thereby providing the magnetic field perpendicular to the cellular anode l2 and cathode plates 13.

As can be seen from the above, the pumping chamber 24 containing the pumping. element 11 is positioned between the pole pieces of each U-shaped magnet 3'7 where the magnetic field is the strongest while the gas access chambers 25 are located deep within the U where the field is weakest thus taking the greatest advantage of the magnets magnetic field while still providing large volumes on the sides of the pumping element 11 for increased pumping speed.

A glow discharge getter ion pump of the type described above with a pumping element approximately 3 x 9 x 1 inches, a potential difference between the anode and cathode of 6 kv., and a magnetic field of 1800 gauss pumps approximately 75 liters of air per second at 1 1O mm. of Hg.

Referring now to FIGS. 6 and 7, there is shown an alternative embodiment of the present invention wherein the envelope 46' comprises a hollow cylindrical first gas access chamber 41 with a plurality of rectangular lesser chambers 42 extending radially outwardly therefrom like the spokes of a wheel. Each lesser chamber 42 constitutes a second gas access chamber 46 in the radial outward portion thereof and a pumping chamber 49 in the portion adjacent the first gas access chamber 41. A pumping element 43 similar to the pumping element 11 described above is longitudinally positioned in the pumping chamber 49' within each of the lesser chambers 42 along the opening between the first gas access chamber 4-1 and the lesser chamber 42 by means of rectangular guide tabs 44 at each end of the pumping assembly 43, these guide tabs 44 being removably positioned within guide retainers 45 carried from the walls of the first gas access chamber 4 1 as by, for example, heliarc welding. The lesser chambers 42 are deeper and longer than the pumping elements 43 whereby the second gas access chambers 46 communicate with the first gas access chamber 41 at the ends of the pumping element 43.

The second gas access chambers d6 are made of such a size that the sum ofthe volumes of all the second gas access chambers 46 is approximately the same as the volume of the first gas access chamber 41 whereby gas molecules under the same pressure will be provided to substantially all of each pumping element to achieve the greatest possible pumping speed from the pumping elements. For example, with a first gas access chamber 41 8 in diameter for an open cross-sectional area of about 50 sq. inches and six second gas access chambers 46 2" x 4" for an open cross-sectional area of 48 sq. inches, the second gas access chambers 46 will provide substantially the same volume of gas to the outside of the pumping elements 43 as the first gas access chamber 41 does to the inside of the pumping elements for a given length of the pumping element. The proper cross-sectional area A for each second gas access chamber 46 to provide the same volume of gas on both sides of the pumping element can be determined from the formula where A is the cross-sectional area or" the first gas access chamber 41 and n is the number of second gas access chambers 46.

The magnetic field for the pump shown in FIGS. 6 and 7 is provided by a plurality of sector-shaped permanent magnets 47 which are radially bored to receive studs 48 therethrough which are fixedly secured as by, for example, spot welding to the envelope 40 and extend radially therefrom. The studs 48 are threaded at their outermost end portions to receive nuts to firmly hold the permanent magnets 47 in position between adjoining lesser rectangu lar chambers 42.

Another embodiment of the present invention is shown in FIG. 8. The view depicted by FIG. 8 is somewhat similar to the view depicted by FIG. 6 of an alternative pump structure. In the embodiment of FIG. 8 the envelope 50 comprises a rectangular shaped first gas access chamber 51 with a number of rectangular lesser chambers 52 extending outwardly therefrom. Each lesser chamber 52 constitutes a second gas access chamber 54 in the radial outward portion thereof and a pumping chamber 58 in the portion adjacent the first gas access chamber 51. As in the structure of FIGS. 6 and 7 each pumping chamber 58 houses a pumping element 53, and the total volume of all the second gas access chambers 54 is approximately the same as the volume of the first gas access chamber 51. For example, with a first gas access chamber 51 square for an open cross-sectional area of 25 sq. inches and four second gas access chambers 54 each 2 x 3 for a total open cross-sectional area of 24 sq. inches the second gas access chambers 54 will provide substantially the same volume to the outside of the pumping elements 53 as the first gas access chamber 51 does to the inside of the pumping elements for the same length of pumping element. The necessary size for each second gas access chamber 54 can be determined by the formula used for the embodiment of FIGS. 6 and 7.

A magnetic field is applied perpendicularly to the pumping elements 53 via a plurality of rectangular permanent magnets 55 stacked in a number of columns, the plane of adjacent columns being disposed substantially at right angles to each other. At the intersection of the columns, the permanent magnets are rigidly connected together via a square rod 56 and are held against rectangular pole pieces 57 positioned on the sides of each pumping chamber 58 by bolts which pass through the rods 56 and the magnets 55 and anchor in tapped holes in the pole pieces 57.

Referring now to FIG. 9 there is the relationship between pumping for an electrical vacuum above.

shown a graph giving speed and conductance pump of the type described In the graph the ordinate is a measure of So o and the abscissa is a measure of 0 where S is the intrinsic pumping speed (i.e. the pumping speed one would have if there were no conductance limitation in the gas access channels), S is the effective speed (i.e. the pump speed actually available at the entrance to the pumping area), and the C is conductance of the channel-s immediately adjacent to the pumping element and providing gas access thereto. The ratio 1 o is determined from the equation tanh flgg S :31 Co As shown in the graph, when the conductance C decreases and therefore the ratio of is no greater than 08 whereby the ratio of the effective pumping speed to the intrinsic pumping speed o is no less than 0.8 thereby providing extremely efiicient pumps. Methods for determining the conductance of different structures are outlined in Chapter 2 of Scientific Foundations of Vacuum Technique by S. Dushman, John Wiley & Sons, Inc., New York, 1949.

While a cellular anode has been utilized to describe the present invention, it is obvious that other workable anode configurations could be used, For example, the anode may comprise a series of parallel plates having a plurality of apertures therein, the apertures being so aligned as to form a plurality of glow discharge passageways confining therewithin glow discharge columns in mutual parallelism extending and directed in the direction of the magnetic field threading the anode and, normal to the cahode plates. All of the anode plates may be supported by two common support members which in turn may be supported from the flanged brackets 14 of the pump described above by means of insulator assemblies such as the insulator assembly 16 decribed above. These and still other shapes and designs for the pumping element are set forth in co-pending application, Serial No, 673,816 filed July 24, 1957, by Lewis D. Hall et 211., now US. Patent 2,993,638, issued July 25, 1961.

Since many changes could be made in the above construotion and many apparently Widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A glow discharge apparatus comprising, in combination, means defining a gas tight envelope defining a pumping chamber and a plurality of gas access chambers, said pumping chamber having two mutually opposed relatively broad side wall portions, all of said gas access chambers communicating with said pumping chamber other than through said broad side walls, and pumping elements disposed substantially parallel to said broad side wall portions for establishing a glow discharge within said pumping chamber, said means defining the gas tight envelope providing an inlet opening communicating with said pumpingcharnber through said gas access chambers whereby direct access is provided to said pumping chamber for a large volume of gas contained in said gas access chambers thereby providing a glow discharge apparatus of large capacity.

2. The glow discharge apparatus of claim 1 wherein said gas access chambers include a central first gas access chamber communicating with the structure it is desired to evacuate and a plurality of lesser chambers communicating with said central first gas access chamber, each of said lesser chambers extending radially outwardly of said central chamber like the spokes of a wheel lengthwise of said central chamber and including a second gas access chamber in the radial outward portion thereof and a pumping chamber in the portion thereof adjacent said central chamber, the sum of the volumes of all of said second gas access chambers being substantially the same as the volume of said central first gas access chamber.

3. A glow discharge apparatus comprising, in combination, means forming a gas tight envelope defining a central pumping chamber and a plurality of gas access side chambers, all of said side gas access chambers communicating with said pumping chamber, said pumping chamber having two mutually opposed relatively broad side wall portions, means within said envelope forming a cathode having spaced apart mutually opposed portions disposed parallel to the broad sides of said pumping chamber, means forming an anode disposed in the plane substantially parallel to said broad side walls of said pumping chamber between and in spaced apart relation from said opposed cathode portions, and means for producing and directing a magnetic field transversely of the plane of said anode means, said means forming the gas tight envelope providing an inlet opening communicating with said pumping chamber through said side gas access chambers whereby direct access is provided to substantially all of the space between said means forming the anode and said means forming the cathode thereby providing a glow discharge apparatus of large volume capacity.

4. The glow discharge apparatus of claim 3 wherein the inlet opening in said envelope communicating with said pumping chamber and all of said side gas access chambers is at least as wide as the width of said pumping chamber whereby said means forming the cathode and said means forming the anode can easily be withdrawn through the inlet opening in said gas tight envelope.

5. The glow discharge apparatus of claim 3 including means forming an insulator assembly supporting said anode means insulated from said mutually spaced apart cathode portions, said insulator assembly including an insulator member provided with a re-entrant portion and a shield surrounding said re-entrant portion to prevent sputtered material from being deposited upon said insulator preventing voltage leakage thereacross.

6. An electrical vacuum pump comprising in combination means forming a gas tight envelope defining a central pumping chamber and a plurality of side gas access chambers, all of said gas access chambers communicating with said central pumping chamber, said central pumping chamber having two mutually opposed relatively broad side wall portions and said side gas access chambers having a transverse cross section in the form of a partially closed semicircle with the communication into said central pumping chamber occupying a portion of the fiat side of the partially closed semicircle, means forming a cathode hay-ing spaced apart mutually opposed portions disposed parallel to said broad sides of said central pumping chamber, means forming an anode disposed in the plane substantially parallel to said broad side walls of said central pumping chamber between and in spaced apart relation from said opposed cathode portions, insulating support means supporting said anode means between said mutually spaced apart cathode portions, said insulating support means including an insulator member provided with a re-entrant portion and a shield s round-ing said re-entrant portion preventing deposit of material upon said insulator therewithin and means for producing and directing a magnetic field transversely of the plane of said anode means, said means for producing and directing the magnetic field including T-shaped pole pieces with the top of the T positioned adjacent said broad side walls of said central pumping chamber, and a pltu'ality of oppositely directed pairs of U-shaped magnets surrounding said side chambers and connected with poles of corresponding polarity to said pole pieces, said means forming the gas tight envelope providing an inlet opening communicating with said central pumping chamber through said side gas access chambers and at least as wide as the width of said central pumping chamber whereby direct access is provided to substantially all of the space between said means forming the anode and said means forming the cathode thereby providing a glow discharge apparatus of large volume capacity and in which the means forming the anode and the means forming the cathode can easily be withdrawn through the opening in said gas tight envelope.

7. A glow discharge apparatus comprising in combination means forming a gas tight envelope defining a central first gas access chamber and a plurality of lesser chambers communicating with and extending radially outwardly from said first gas access chamber, each of said lesser chambers constituting a second gas access chamber in the radial outward portion thereof and a pumping chamber in the portion adjacent said first gas access chamber, said pumping chambers having two mutually opposed relatively broad side wall portions, means within each of said pumping chambers forming a cathode having spaced apart mutually opposed portions disposed parallel to said broad side walls of said respective pumping chambers, means forming an anode disposed in the plane substantially parallel to said broad side walls of said respective pumping chambers between and in spaced apart relation from said opposed cathode portions, and means for producing and directing a magnetic field transversely of the plane of said respective anode means, said means forming the gas tight envelope providing an inlet opening communicating with said pumping chamber through said gas access chambers whereby direct access is provided to said pumping chambers for a large volume of gas contained in said gas access chambers thereby providing a glow discharge: apparatus of large volume capacity.

8. An electrical vacuum pump comprising in combination means forming a gas tight envelope defining a central pumping chamber and a plurality of side gas access chambers, all of said gas access chambers communicating with said central pumping chamber, said central pumping chamber having two mutually opposed relatively broad side wall portions and said side gas access chambers having a transverse cross section in the form of a partially closed semicircle with the communication into said central pumping chamber occupying a portion of the flat side of the partially closed semicircle, means forming a cathode having spaced apart mutually opposed portions disposed parallel to said broad sides of said central pumping chamber, means forming an anode disposed in the plane substantially parallel to said broad side walls of said central pumping chamber between and in spaced apart relation from said opposed cathode portions, insulating support means supporting said anode'means between said mutually spaced apart cathode portions, said insulating support means including an insulator member provided with a redischarge apparatus of large volume capacity and in which the means forming the anode and the means form,- ing the cathode can easily be Withdrawn through the opening in said gas tight envelope.

References Cited in the file of this patent UNITED STATES PATENTS 1,146,298 Ambruster July 13, 1915 1,924,056 Benit Aug. 22, 1933 2,085,735 Brion et al. July 6, 1937 2,279,586 Bennett Apr. 14, 1942 

1. A GLOW DISCHARGE APPARATUS COMPRISING, IN COMBINATION, MEANS DEFINING A GAS TIGHT ENVELOPE DEFINING A PUMPING CHAMBER AND A PLURALITY OF GAS ACCESS CHAMBERS, SAID PUMPING CHAMBER HAVING TWO MUTUALLY OPPOSED RELATIVELY BROAD SIDE WALL PORTIONS, ALL OF SAID GAS ACCESS CHAMBERS COMMUNICATING WITH SAID PUMPING CHAMBER OTHER THAN THROUGH SAID BROAD SIDE WALLS, AND PUMPING ELEMENTS DISPOSED SUBSTANTIALLY PARALLEL TO SAID BROAD SIDE WALL PORTIONS FOR ESTABLISHING A GLOW DISCHARGE WITHIN SAID PUMPING CHAMBER, SAID MEANS DEFINING THE GAS TIGHT ENVELOPE PROVIDING AN INLET OPENING COMMUNICATING WITH SAID PUMPING CHAMBER THROUGH SAID GAS ACCESS CHAMBERS WHEREBY DIRECT ACCESS IS PROVIDED TO SAID PUMPING CHAMBER FOR A LARGE VOLUME OF GAS CONTAINED IN SAID GAS ACCESS CHAMBERS THEREBY PROVIDING A GLOW DISCHARGE APPARATUS OF LARGE CAPACITY. 